(654c) Tandem Electrocatalytic and Thermocatalytic Reactors for CO2 Conversion to BTEX Aromatics

Sustainable CO₂ conversion is a promising strategy for carbon reduction and utilization as we push to reduce the atmospheric CO₂ concentration and limit global warming to 1.5 ºC. Replacing fossil fuels with CO₂ as a major feedstock for the chemical supply chain allows alcohols, plastics, fertilizers, and many other products that are integral to modern society to be produced with significantly reduced environmental impacts. Electrochemical CO₂ reduction (CO₂R) has been widely studied as method for sustainable CO₂ valorization, but real-world implementation of electrochemical CO₂R is limited by low selectivities for valuable multicarbon products and low production rates of complex products including oxygenates and aromatics. However, coupling electrocatalytic CO₂R with a downstream thermocatalytic reaction that is compatible with a mixture of CO₂R products enables the production of complex products with high selectivities, thus overcoming the limitations of direct electrochemical CO₂R. In this work, we present a tandem reactor scheme wherein CO₂ is electrochemically reduced in a membrane electrode assembly (MEA) to produce ethylene (C₂H₄), which subsequently undergoes thermocatalytic aromatization over a gallium- and phosphorus-modified ZSM-5 catalyst (Ga/ZSM-5/P) to produce a mixture of benzene, toluene, ethylbenzene, and xylene isomers (BTEX). Several copper and copper oxide catalysts are assessed for their electrocatalytic performance in a 5 cm² MEA by measuring polarization curves and quantifying the product distributions using gas chromatography. We show that Cu is the optimal electrocatalyst, as it exhibits the highest C₂H₄ selectivity and lowest absolute cell voltage of all the catalysts tested. The viability of the full tandem reactor system for CO₂ conversion to aromatics is then demonstrated by directly feeding the MEA output into a thermochemical flow reactor with Ga/ZSM-5/P (2 wt% Ga, 0.8 wt% P) at 650 ºC. Finally, we present a parametric study of electrocatalyst loadings, current densities, and CO₂ flow rates to optimize overall BTEX yield.